Pituitary adenylate cyclase-activating polypeptide (PACAP): occurrence in rodent pancreas and effects on insulin and glucagon secretion in the mouse

Summary Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that occurs in several tissues, e.g., in the gut. We have studied PACAP-like immunoreactivity in the pancreas of rat and mouse, and the effects of PACAP-38 on basal and stimulated insulin and glucagon secretion in the mouse. Immunofluorescence staining demonstrated the presence of PACAP-like immunoreactivity in nerve fibers in both the rat and mouse pancreas. The nerve fibers were seen in the exocrine pancreas and surrounding the islets. Occasionally, the nerve fibers occurred within the islets. Most PACAP-positive nerve fibers innervated the intrapancreatic ganglia, although no nerve cell bodies contained PACAP-like immunoreactivity. In-vivo experiments in mice revealed that basal plasma glucagon levels were increased by PACAP-39 injected intravenously at dose levels exceeding 1.8 nmol/kg. Furthermore, PACAP-38 (7 nmol/kg) potentiated the plasma glucagon response to the cholinergic agonist carbachol (0.16 mol/kg). This potentiation was reduced to simple addition by pretreatment with a combined - and -adrenergic blockade by phentolamine (35 mol/kg) and propranolol (8.5 mol/kg). Moreover, PACAP-38 inhibited a carbachol-induced increase in the level of plasma insulin in the absence but not in the presence of adrenergic blockade. PACAP-38 increased basal plasma insulin levels and increased basal plasma glucose levels 6 min and 10 min, respectively, after injection of the peptide. We conclude that PACAP-like immunoreactivity exists in nerve fibers innervating the mouse and rat pancreas, particularly the intrapancreatic ganglia, and that PACAP-38 augments both basal and carbachol-stimulated glucagon secretion in the mouse.     

Peripheral and central alterations of pituitary adenylate cyclase activating polypeptide-like immunoreactivity in the rat in response to activation of the trigeminovascular system

Pituitary adenylate cyclase activating polypeptide (PACAP) is present in the cranial arteries and trigeminal sensory neurons. We therefore examined the alterations in PACAP-like immunoreactivity (PACAP-LI) in a time-dependent manner in two rat models of trigeminovascular system (TS) activation. In one group chemical stimulation (CS) was performed with i.p. nitroglycerol (NTG), and in the other one the trigeminal ganglia (TRG) were subjected to electrical stimulation (ES). The two biologically active forms, PACAP-38 and PACAP-27, were determined by means of radioimmunoassay (RIA) and mass spectrometry (MS) in the plasma, the cerebrospinal fluid (CSF), the trigeminal nucleus caudalis (TNC), the spinal cord (SC) and the TRG. The tissue concentrations of PACAP-27 were 10 times lower than those of PACAP-38 in the TNC and SC, but about half in the TRG. PACAP-38, but not PACAP-27, was present in the plasma. Neither form could be identified in the CSF. PACAP-38-LI in the plasma, SC and TRG remained unchanged after CS, but it was increased significantly in the TNC 90 and 180 min after NTG injection. In response to ES of the TRG, the level of PACAP-38 in the plasma and the TNC was significantly elevated 90 and 180 min later, but not in the SC or the TRG. The alterations in the levels of PACAP-27 in the tissue homogenates in response to both forms of stimulation were identical to those of PACAP-38. The selective increases in both forms of PACAP in the TNC suggest its important role in the central sensitization involved in migraine-like headache.     

Naloxone and methylprednisolone sodium succinate enhance sympathomedullary discharge in patients with septic shock

Naloxone and methylprednisolone sodium succinate (MPSS) may act in synergy to improve hemodynamics in patients with septic shock by enhancement of sympathomedullary discharge. This randomized double-blind study describes the effect of various dosing regimens of naloxone and MPSS upon hemodynamics and plasma catecholamines in patients with septic shock (n = 57). Consecutive bolus doses of naloxone were given 30 minutes apart (10 μg/kg;–100 μg/kg) and a single dose of MPSS (30 mg/kg); bolus doses of 5% dextrose in water solution plus single dose of MPSS as above; bolus dose of naloxone (30 μg/kg) followed by continuous infusion (30 μg/kg/hr for 1 hour) with single dose of MPSS as above; a bolus and continuous infusion of naloxone as above without MPSS; MPSS alone and standard therapy alone. In patients treated with bolus doses of naloxone in combination with MPSS, plasma levels of epinephrine and norepinephrine were increased approximately five-to tenfold. In patients treated with bolus plus continuous infusion of naloxone given with or without MPSS, only plasma epinephrine levels were increased. Systolic blood pressure and left ventricular stroke work index were improved within 15 minutes in groups which received naloxone and corticosteroids regardless of dose. In those groups, there were no changes in heart rate or filling pressure. Systematic vascular resistance improved significantly only in the group which received low dose bolus and continuous infusion of naloxone and MPSS. Naloxone and MPSS quickly improved cardiac function in patients with septic shock by enhanced sympathomedullary discharge and may be useful as an adjunct in the therapy of this disorder.     

The influence of hormones and inflammatory agents on C-reactive protein, cortisol and alanine aminotransferase in the plaice (Pleuronectes platessa L.)

Endotoxin stimulates production of both C-reactive protein (CRP) and cortisol in the plaice within 24 hr. Cortisol alone (optimum dose i.p. 500 micrograms/300 g wt fish) also stimulates CRP production and the possibility that endotoxin acts through cortisol was examined. Dexamethasone suppresses cortisol production but elevates CRP. Cortisol levels are restored to normal within 24 hr of endotoxin injection. Turpentine and ACTH which stimulate cortisol do not affect CRP. Endotoxin and cortisol have no significant effect on alanine aminotransferase activity in the serum and liver although it is elevated in the serum within 24 hr of the administration of adrenalin or turpentine.     

Neuropeptides of the vasoactive intestinal peptide/helodermin/pituitary adenylate cyclase activating peptide family elevate plasma cAMP in mice: comparison with a range of other regulatory peptides

A number of regulatory peptides were investigated for their ability to elevate plasma cAMP. Pituitary adenylate cyclase activating peptide (PACAP)-27, PACAP-38, helodermin, helospectin I and II, vasoactive intestinal peptide (VIP), glucagon, parathyroid hormone (PTH), calcitonin and calcitonin gene-related peptide were among the peptides that were highly effective in raising plasma cAMP when given intravenously in equimolar doses to conscious mice. PACAP-27 and -38 were more effective than any of the other peptides. PACAP 16–38, secretin, gastrin-17, galanin, somatostatin, cholecystokinin-8s, pancreatic polypeptide, substance P, peptide YY and neuropeptide Y were inactive and also did not interfere with the PACAP-27-evoked rise in plasma cAMP levels. Repeated injections of PACAP-27 every 30 min caused a progressive reduction in the plasma cAMP response (measured 5 min after each injection). Forskolin, an activator of adenylate cyclase, dose-dependently raised the plasma concentration of cAMP and displayed a synergistic effect when given in a low dose concurrently with PTH or PACAP-38. The phosphodiesterase inhibitor rolipram dose-dependently raised the plasma concentration of cAMP. Combined treatment with PACAP-27 and a threshold dose of rolipram resulted in an exaggerated plasma cAMP response. Kidney hilus ligation suppressed the responses to PACAP-38, PTH, helodermin, helospectin, VIP, glucagon and calcitonin. Hepatectomy suppressed the response to glucagon but was without effect on the response to the other peptides. Pancreatectomy and spleenectomy reduced the response to VIP, but was without effect on the response to the other peptides. PACAP-27 stimulated cAMP efflux from the isolated rat tail vein. Hence, it cannot be excluded that blood vessels contribute to the peptide evoked plasma cAMP response in vivo.     

PACAP-(1-38) as neurotransmitter in the porcine adrenal glands

The concentration of pituitary adenylyl cyclase-activating polypeptide [PACAP-(1-38)] in porcine adrenal glands amounted to 14 +/- 3 pmol/g tissue. PACAP immunoreactive (PACAP-IR) fibers innervated adrenal chromaffin cells (often co-localized with choline acetyltransferase). Subcapsular fibers traversed the cortex-innervating endocrine cells and blood vessels [some co-storing mainly calcitonin gene-related peptide but also vasoactive intestinal polypeptide (VIP)]. PACAP-IR fibers were demonstrated in the splanchnic nerves, whereas IR adrenal nerve cell bodies were absent. In isolated, vascularly perfused adrenal gland, splanchnic nerve stimulation (16 Hz) and capsaicin (10(-5) M) increased PACAP-(1-38) release (1.6-fold and 6-fold respectively, P = 0.02). PACAP-(1-38) dose-dependently stimulated cortisol (2 x 10(-10) M; 24-fold increase, P = 0.02) and chromogranin A fragment (2 x 10(-9) M; 15-fold increase, P = 0.05) secretion. Both were strongly inhibited by the PAC(1)/VPAC(2) receptor antagonist PACAP-(6-38) (10(-7) M). PACAP-(6-38) also inhibited splanchnic nerve (10 Hz)-induced cortisol secretion but lacked any effect on splanchnic nerve-induced pancreastatin secretion. PACAP-(1-38) (2 x 10(-10) M) decreased vascular resistance from 5.5 +/- 0.6 to 4.6 +/- 0.4 mmHg. min. ml(-1). PACAP-(6-38) had no effect on this response. We conclude that PACAP-(1-38) may play a role in splanchnic nerve-induced adrenal secretion and in afferent reflex pathways.     

刺激腓深神经对低血压或休克狗心血管活动的影响

实验在麻醉狗中进行。静脉内匀速注射硝普钠时,平均动脉压和左心室收缩压明显降低,左心室dp/dt_(max)、-dp/dt_(max)和心力环面积均明显减小。此时电刺激一侧腓深神经可使动脉血压和左心室收缩压明显升高,dp/dt_(max)和心力环面积也显著增加。停止刺激后,动脉血压和左心室收缩压逐渐回向刺激前的水平。停止注射硝普钠5～15分钟后,上述各项观察指标基本恢复到注药前的水平。在用大肠杆菌内毒素造成休克的狗中,电刺激一侧腓深神经,也能使平均动脉压和左心室收缩压升高,同时dp/dt_(max)、-dp/dt_(max)和肠系膜血管阻力明显增高,但肾血管阻力增加不明显。本实验结果与以往的实验资料一起表明,在用扩血管药造成低血压时,躯体神经刺激引起的升压效应似乎以心肌收缩力增加为主;而在内毒素休克时,躯体神经刺激可通过改善心肌收缩功能和增加内脏血管阻力而引起升压作用。     

Effect of short-term intralipid infusion on the immune response during low-dose endotoxemia in humans

Novel anti-inflammatory effects of insulin have recently been described, and insulin therapy to maintain euglycemia suppresses the plasma levels of free fatty acids (FFA) and increases the survival of critically ill patients. We aimed to explore the effect of short-term high levels of plasma FFA on the inflammatory response to a low dose of endotoxin. Fourteen healthy male volunteers underwent the following two trials in a randomized crossover design: 1) continuous infusion of 20% Intralipid [0.7 ml.kg(-1).h(-1) (1.54 g/kg)] for 11 h, and 2) infusion of isotonic saline for 11 h (control). In each trial, heparin was given to activate lipoprotein lipase, and an intravenous bolus of endotoxin (0.1 ng/kg) was given after 6 h of Intralipid/saline infusion. Blood samples and muscle and fat biopsies were obtained before the Intralipid/saline infusion and before as well as after infusion of an endotoxin bolus. Plasma levels of FFA, triglycerides, and glycerol were markedly increased during the Intralipid infusion. Endotoxin exposure induced an increase in plasma levels of TNF-alpha, IL-6, and neutrophils and further stimulated gene expression of TNF-alpha and IL-6 in both skeletal muscle and adipose tissue. The systemic inflammatory response to endotoxin was significantly pronounced during Intralipid infusion. Short-term hyperlipidemia enhances the inflammatory response to endotoxin, and skeletal muscle and adipose tissue are capable of producing essential inflammatory mediators after endotoxin stimulation.     

Anti-inflammatory effects of ergotamine in steers

The objective of this experiment was to investigate whether the ergot alkaloid, ergotamine (ET), an alkaloid used to model fescue toxicosis in cattle, modifies the response of cattle to endotoxin (LPS) challenge. Steers (n = 16) were divided into the following treatment groups: control (C), ergotamine (ET), endotoxin (LPS), and ET + LPS. ET and ET + LPS groups received a single bolus intravenous injection of ET (40 microg. kg. body wt(-1)), whereas C and LPS steers received a single bolus injection of sterile vehicle. Thirty minutes after ET/vehicle administration, a single bolus intravenous injection of LPS (0.2 microg. kg. body wt(-1)) was given. Blood was collected at various time points for 48 hr post. Endotoxin increased rectal temperature (RT) and the circulating levels of tumor necrosis factor-alpha (TNF-alpha), cortisol, haptoglobin (Hp), thromboxane B(2) (TXB(2)). The circulating Hp, TNF-alpha, and TXB(2) increases were blunted by pretreatment with ET compared with ET + LPS. Ergotamine by itself increased circulating cortisol and RT, whereas it decreased serum prolactin (PRL). Therefore, whereas administration of LPS at 0.2 microg/kg to steers resulted in an expected response, the combination of ET + LPS attenuated major effects of LPS alone. Thus, acute administration of ET appeared to be anti-inflammatory as it decreased the inflammatory response to LPS, an effect likely driven at least in part by the ET-caused cortisol increase.     

Cardiovascular effects of intravenous ghrelin infusion in healthy young men

Ghrelin infusion improves cardiac function in patients suffering from cardiac failure, and bolus administration of ghrelin increases cardiac output in healthy subjects. The cardiovascular effects of more continuous intravenous ghrelin exposure remain to be studied. We therefore studied the cardiovascular effects of a constant infusion of human ghrelin at a rate of 5 pmol/kg per minute for 180 min. Fifteen healthy, young (aged 23.2 +/- 0.5 yr), normal-weight (23.0 +/- 0.4 kg/m(2)) men volunteered in a randomized double-blind, placebo-controlled crossover study. With the subjects remaining fasting, peak myocardial systolic velocity S', tissue tracking TT, left ventricular ejection fraction EF, and endothelium-dependent flow-mediated vasodilatation were measured. Ghrelin infusion increased S' 9% (P = 0.002) and TT 10% (P < 0.001), whereas EF, resting blood flow velocity, and endothelium-dependent flow-mediated vasodilatation did not change (P = 0.13). This was associated with a peak in serum growth hormone after 60 min of infusion (37.77 +/- 5.27 ng/ml, P < 0.001), a doubling of free fatty acid levels (P = 0.001), and a 1.6-fold increase in cortisol levels (P < 0.05), whereas glucose and catecholamine levels were constant. In conclusion, supraphysiological levels of ghrelin stimulate left ventricular function in terms of S' and TT in healthy young normal-weight men without changing resting blood flow velocity and endothelium-dependent flow-mediated vasodilatation. The effects did not translate into detectable increments in EF.     

Effects of synthetic ovine corticotropin-releasing factor (CRF) on plasma ACTH and cortisol in 31 normal human males

Responses of plasma ACTH and cortisol to corticotropin-releasing factor (CRF) were evaluated in 31 normal human males. 1.0 micrograms/ks of sterilized synthetic ovine CRF was administered to the subjects, aged 19 to 53 yr and weighing 50 to 78 kg, at between 9:30 a.m. and 10:30 a.m. as an intravenous bolus injection after an overnight fast. Blood specimens were drawn before and 15, 30, 60, 90 and 120 min after injection for later determination of plasma ACTH and cortisol concentrations by radioimmunoassays. Plasma ACTH and cortisol levels for all subjects rose significantly (p less than 0.001) from the basal level (mean +/- SEM, 26.8 +/- 4.5 pg/ml and 12.6 +/- 0.9 micrograms/dl) to peak levels (58.4 +/- 5.5 pg/ml and 22.9 +/- 1.0 micrograms/dl) at 30 min and at 60 min, respectively. Although the plasma concentrations of ACTH and cortisol thereafter declined gradually, the levels at 120 min (43.4 +/- 5.2 pg/ml and 18.9 +/- 0.9 micrograms/ml, respectively) were still significantly higher than the basal levels (p less than 0.001). Significant inverse correlations were observed between the basal levels of each hormone and the ratio of the peak level to the basal level (p less than 0.01), and the increases in plasma ACTH and cortisol concentrations were either not significant or much smaller for the individuals in whom the basal levels were higher than 65 pg/ml and 17.0 micrograms/dl, respectively. No serious subjective symptom was observed during the experimental period in any of the subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermal recovery after passage of the pulmonary circulation assessed by deconvolution

We determined the effect of H2O2 on both the physiological and biochemical lung changes seen in the adult sheep after endotoxin. Fourteen unanesthetized adult sheep with chronic lung lymph fistula were given Escherichia coli endotoxin (1 microgram/kg) over 30 min. Seven sheep were given catalase (32,500 U/kg body wt) as an intravenous bolus 30 min before endotoxin. Four sheep were given catalase alone. Oxidant lung changes were measured using arterial plasma conjugated dienes and lung tissue malondialdehyde (MDA) content, both reflecting the lipid peroxidation process. Animals were killed 5 h after endotoxin. We found that endotoxin alone caused an early increase in pulmonary arterial pressure lung lymph flow (QL), plasma thromboxane B2, 6-keto-prostaglandin F1 alpha, and plasma conjugated dienes. A decrease in cardiac output and arterial PO2 was also seen. A three- to four-fold increase in protein-rich QL was noted at 3-4 h as well as a continued increase in arterial conjugated dienes. Lung MDA and water content were also significantly increased from base line. Catalase pretreatment significantly attenuated both the physiological changes and the prostanoid and conjugated diene release. Lung MDA and water content also remained at base line. We conclude that H2O2 plays a major role in endotoxin-induced lung injury as well as the resulting lipid peroxidation process.     

Effect of synthetic ovine corticotropin-releasing factor on growth hormone secretion in patients with acromegaly

In a significant proportion of patients with acromegaly, a non-specific increase in plasma growth hormone (GH) has been recognized following administration of thyrotropin-releasing hormone (TRH) or luteinizing hormone-releasing hormone (LH-RH), probably due to the lack of the specificity of the receptor in their tumor cells. In this study, the effects of corticotropin-releasing factor (CRF), a newly isolated hypothalamic hormone, in addition to TRH and LH-RH, on plasma levels of GH and the other anterior pituitary hormones were evaluated in 6 patients with acromegaly. Synthetic ovine CRF (1.0 microgram/kg), TRH (500 micrograms) or LH-RH (100 micrograms) was given as an iv bolus injection, in the morning after an overnight fast. Blood specimens were taken before and after injection at intervals up to 120 min, and plasma GH, adrenocorticotropin (ACTH), thyrotropin, prolactin, luteinizing hormone, follicle-stimulating hormone and cortisol were assayed by radioimmunoassays. A non-specific rise in plasma GH was demonstrated following injection of TRH and LH-RH, in 5 of 6 and 2 of 5 patients, respectively. In all subjects, rapid rises were observed in both plasma ACTH (34.3 +/- 6.2 pg/ml at 0 min to 79.5 +/- 9.5 pg/ml at 30 min, mean +/- SEM) and cortisol level (9.1 +/- 1.3 micrograms/dl at 0 min to 23.4 +/- 1.2 micrograms/dl at 90 min). However, plasma levels of GH and the other anterior pituitary hormones did not change significantly after CRF injection. These results indicate that CRF specifically stimulates ACTH secretion and any non-specific response of GH to CRF appears to be an infrequent phenomenon in this disorder.     

Endotoxic shock in the piglet: beneficial effects of prostaglandin synthesis inhibition

In anesthetized piglets the intravenous injection of a lethal dose of endotoxin, 0.5 mg/kg, resulted in a progressively evolving deterioration of the cardiovascular system (hypotension, decrease in cardiac output), in an increase in pulmonary vascular resistance and in the death of all animals within 210 min following endotoxin administration. Endotoxin induced a significant increase in immunoreactive (i) i-6-oxo-PGF_1α, i-TXB₂, and i-15-oxo-13,14-dihydro-PGF_2α levels in peripheral plasma. Pretreatment with the PG-synthesis inhibitor, flurbiprofen, abolished the profound rise in PG-levels, whereas cardiovascular performance was more sustained. The results suggest the involvement of several prostanoids during the evolution of endotoxic shock in the piglet.     

Recombinant glucagon-like peptide-1 (7-36 amide) lowers fasting serum glucose in a broad spectrum of patients with type 2 diabetes.

AIMS: To evaluate the safety and efficacy of various doses of recombinant glucagon-like peptide-1 (7-36) amide (rGLP-1) administered subcutaneously (s. c.) via bolus injection or continuous infusion to lower fasting serum glucose (FSG) levels in subjects with type 2 diabetes treated by diet, hypoglycemic drugs, or insulin injection. METHODS: rGLP-1 was administered s. c. to 40 type 2 diabetics currently treated by diet, sulfonylurea (SU), metformin, or insulin in a double-blind, placebo-controlled, cross-over trial; preexisting treatments were continued during the study. In the bolus injection protocol, 32 subjects (8 from each of the 4 treatment groups) received 0.0, 0.5, 1.0, and 1.5 nmol rGLP-1/kg per injection (two injections, two hours apart, beginning one hour after the evening meal) in a randomized order on separate days. In the continuous s. c. infusion protocol, 40 subjects received rGLP-1 at 0.0, 1.5, 2.5, 3.5, and 4.5 pmol/kg/min for 10-12 hours overnight starting one hour after the evening meal. Fasting bloods were taken the morning after for glucose, insulin, and glucagon measurements. RESULTS: In the diet, SU, and metformin cohorts, bolus rGLP-1 injections produced modest reductions in mean FSG levels, averaging 17.4 mg/dl (7.3-27.5; 95 % CI) at the highest dose (p < 0.001 vs. placebo). Reductions in FSG levels were greater by continuous infusion at up to 30.3 mg/dl (18.8 - 41.8; 95 % CI; p < 0.001 vs. placebo). The greatest reduction in mean FSG occurred in the SU cohort (up to 43.9 mg/dl, 24.7 - 63.1; 95 % CI; p < 0.001). rGLP-1 infusions resulted in significant increases in fasting plasma insulin and decreases in fasting plasma glucagon levels. There were no serious adverse events; GI-related symptoms were dose-related and more commonly associated with injections. CONCLUSIONS: rGLP-1 (7-36) amide dose-dependently lowered FSG in a broad spectrum of type 2 diabetics when added to their existing treatment. Subcutaneous infusion was more effective than injection, and the combination with SU was more effective than with metformin.     

PACAP release from the canine adrenal gland in vivo: its functional role in severe hypotension

This study was to investigate if endogenous pituitary adenylate cyclase-activating polypeptide (PACAP) can be released during direct splanchnic nerve stimulation in vivo and to determine whether PACAP in the adrenal gland can modulate the medullary response to sympathoadrenal reflex. The output of adrenal catecholamine and PACAP-38-like immunoreactivity (PACAP-38-ir) increased in a frequency-dependent manner after direct splanchnic nerve stimulation (0.2-20 Hz). Both responses were highly reproducible, and PACAP-38-ir output closely correlated with catecholamine output. Sodium nitroprusside (SNP; 0.1 mg/kg iv bolus) caused a severe hypotension resulting in marked increases in catecholamine secretion. In the presence of local PACAP-27 (125 ng), the maximum catecholamine response to SNP was significantly potentiated in a synergistic manner compared with that obtained in the group receiving SNP or PACAP-27 alone. The study indicates that endogenous PACAP-38 can be released particularly when the sympathoadrenal system is highly activated and that the local exogenous PACAP-27 enhanced the reflex-induced catecholamine release, suggesting collectively a facilitating role of PACAP as neuromodulator in the sympathoadrenal function in vivo.     

Responses of plasma adrenocorticotropin and cortisol to intravenous injection of synthetic ovine corticotropin releasing factor in the morning and early evening in normal human subjects

This study was designed to compare the responsiveness of adrenocorticotropin (ACTH) and cortisol secretion to corticotropin-releasing factor (CRF) in the morning and early evening in normal human subjects. Synthetic ovine CRF (1.0 micrograms/kg) or normal saline, was administered as an i.v. bolus injection to six normal males at 900 h and 1700 h. Blood samples were obtained before and 15, 30, 60, 90 and 120 min after CRF or saline injection. Significant increases in plasma ACTH and cortisol levels were observed in all subjects at the both time of testing after CRF injection. The net increments in the areas under the concentration curve (areas in the CRF experiment minus those in the saline control experiment) were not statistically different for both ACTH (mean +/- SEM: 41.0 +/- 10.6 pg/ml h in the morning: 51.1 +/- 8.9 pg/ml h in the evening) and cortisol (mean +/- SEM: 28.5 +/- 5.0 micrograms/dl h in the morning; 36.2 +/- 4.0 micrograms/dl h in the evening). Also no significant difference was observed in net increment, peak level and the ratio of peak level to the basal level of ACTH and cortisol after CRF injection. There were no appreciable changes in plasma concentrations of growth hormone, thyroid-stimulating hormone or prolactin, although slight but statistically significant rises in plasma levels of luteinizing hormone and follicle-stimulating hormone were observed. These results suggest that there is no significant difference in responsiveness of the pituitary-adrenal axis to CRF in the morning (900 h) and early evening (1700 h), and thus the time of day will not necessarily have to be considered when CRF is used between these times in a clinical test to evaluate pituitary ACTH reserve.     

Vascular effects, formation, clearance and release of endothelin peptides in the pig

The formation, release, clearance and vascular effects of endothelin (ET)-like immunoreactivity (-LI) was studied in the pig in vivo. Intravenous infusion of ET-1, 2 and 3 (20 pmol/kg/min for 20 min) increased vascular resistance in the kidney, spleen and skeletal muscle. The most pronounced effects were evoked by ET-1 which caused increases in renal, splenic and skeletal muscle vascular resistance of 554, 528 and 38%, respectively, and a threshold response was observed at 80 pmol/l ET-LI in arterial plasma. During the infusion a large portion of arterial plasma, ET-LI was cleared over the kidney, spleen and skeletal muscle, whereby the most pronounced clearance was observed for ET-1 (73–93%). The ET-1 precursor Big-ET (1–39) given in a similar dose produced only a slight increase in renal vascular resistance (by 20%) and was cleared only over the kidney and not over the spleen or skeletal muscle. Using an ET-1 specific antiserum it was found that plasma ET-1 levels increased 11-fold during the infusion of Big-ET, indicating formation of ET-1 from Big-ET. The half-lives of circulating ET-1, 2 and 3 were 1.3–2.1 min and of Big-ET 8.9 min. Induction of asphyxia for 2 min increased the overflow of ET-LI from the spleen, suggesting local release, and caused splenic vasoconstriction. During i.v. administration of endotoxin for 4 h, arterial plasma ET-LI increased 7-fold and renal and splenic vasoconstrictor responses developed that correlated significantly with the arterial plasma ET-LI. Furthermore, a local release of ET-LI in the spleen was observed during endotoxin administration. Chromatographic characterization of the ET-LI in plasma during endotoxin administration revealed presence of ET-1 and Big-ET. It is concluded that there exists specificity both concerning the vasoconstrictor effects and removal from the circulation of ET peptides, both mechanisms being most prominent for ET-1 in the kidney. Furthermore ET-1 seems to be formed from circulating Big-ET and release of ET-LI can be detected during situations like asphyxia and sepsis.     

Diaspirin cross-linked hemoglobin improves oxygen extraction capabilities in endotoxic shock.

We studied the effects of diaspirin cross-linked hemoglobin (DCLHb), a cell-free hemoglobin derived from human erythrocytes, on blood flow distribution and tissue oxygen extraction capabilities in endotoxic shock. Eighteen pentobarbital sodium-anesthetized, mechanically ventilated dogs received 2 mg/kg of E. coli endotoxin, followed by saline resuscitation to restore cardiac filling pressures to baseline levels. The animals were randomly divided into three groups: six served as control, six received DCLHb at a dose of 500 mg/kg (group 1) and six DCLHb at a dose of 1,000 mg/kg (group 2). Cardiac tamponade was then induced by saline injection in the pericardial sac to progressively reduce cardiac index and thereby allow study of tissue oxygen extraction capabilities. DCLHb had a dose-dependent vasopressor effect but did not significantly alter cardiac index or regional blood flow. During cardiac tamponade, critical oxygen delivery was 12.8 +/- 0.7 ml. kg(-1). min(-1) in the control group, but 8.6 +/- 0.9 and 8.2 +/- 0.7 ml. kg(-1). min(-1) in groups 1 and 2, respectively (both P < 0.05 vs. control group). The critical oxygen extraction ratio was 39.1 +/- 3.1% in the control group but 58.7 +/- 12.8% and 60.2 +/- 9.0% in groups 1 and 2, respectively. We conclude that DCLHb can improve whole body oxygen extraction capabilities during endotoxic shock in dogs.     

Cardiovascular actions of lungfish bradykinin in the unanaesthetised African lungfish, Protopterus annectens

Bradykinin (BK) isolated from plasma of the African lungfish, Protopterus annectens, contains four amino acid substitutions compared with BK from mammals (Arg(1)-->Tyr, Pro(2)-->Gly, Pro(7)-->Ala, Phe(8)-->Pro). Bolus intra-arterial injections of synthetic lungfish BK (1-1000 pmol/kg body wt.) into unanaesthetised, juvenile lungfish (n=5) produced a dose-dependent increase in arterial blood pressure and pulse pressure. The maximum pressor response occurred 2-3 min after injection and persisted for up to 15 min. The threshold dose producing a significant (P<0.01) rise in pressure was 50 pmol/kg and the maximum increase, following injection of 300 pmol/kg, was 9.3 +/- 2.3 mmHg. Injection of the higher doses of lungfish BK produced a significant (P<0.05) increase in heart rate (2.8 +/- 0.8 beats/min at 100 pmol/kg). In contrast, bolus intra-arterial injections of mammalian BK, in doses up to 1000 pmol/kg, produced no significant cardiovascular effects in the lungfish. The data support the existence of a functioning kallikrein-kinin system in the lungfish and demonstrate that the ligand-binding properties of the receptor(s) mediating the cardiovascular actions of lungfish BK are appreciably different from mammalian B1 and B2 receptors.